Hitherto, a device is known that transmits an output torque of an engine to a transmission through a torque converter (for instance, refer to Patent Document 1). The device described in this Patent Document 1 calculates a speed ratio, which is a ratio of rotation speeds on an input shaft side and an output shaft side of the torque converter, and automatically shifts up or down the transmission, when the speed ratio reaches a predetermined value set beforehand.    Patent Document 1: Japanese Patent No. 3388594